This invention relates to an apparatus for preparing a coffee extract with a fine-bubble froth layer, provided with at least one inlet to which coffee extract is supplied, at least one outlet for dispensing, the coffee extract with the fine-bubble froth layer and at least one liquid flow path extending from the at least one inlet to the at least one outlet and along which, in use, the coffee extract flows from the at least one inlet to the at least one outlet, while in the liquid flow path a liquid impact surface is included and the at least one inlet is provided with at least one spout opening for generating at least one coffee extract jet which, in use, squirts to the liquid impact surface when the coffee extract is supplied to the at least one inlet.
Such an apparatus is known per se from the European patent application no. 0 878 158. In the known apparatus, in the liquid flow path a receiving reservoir is included with an upright sidewall and a bottom, the bottom of the receiving reservoir forming the impact surface, so that the coffee extract jet, in use, squirts into the receiving reservoir. Upon the coffee extract jet squirting into the receiving reservoir, a fine-bubble froth layer (also called cafxc3xa9 crxc3xa8me) will be formed as a result of the impingement of the coffee extract jet on the impact surface and in particular through impingement of the coffee extract jet on the liquid surface of a layer of coffee extract located in the receiving reservoir and previously supplied to the receiving reservoir. A cafxc3xa9 crxc3xa8me comprises air-filled coffee bubbles floating on the coffee surface, here called the fine-bubble froth layer. The coffee extract with the thus formed fine-bubble froth layer in the receiving reservoir will subsequently flow from the receiving reservoir to the at least one outlet and can thus be supplied to a holder for coffee, such as, for instance, a cup.
Although the apparatus is most satisfactory, there is the wish to still further improve the apparatus, such that an even more predictable fine-bubble froth layer is formed. By this is meant that the fine-bubble froth layer has a uniform character, the variation of the large ones of the bubbles in the froth layer being relatively small. By this is additionally meant that the relevant fine-bubble froth layer is dispensed in a uniformly repeated manner. In other words, when preparing a new amount of coffee extract with a fine-bubble froth layer, it will be at least substantially the same as an amount of coffee extract with a fine-bubble froth layer previously prepared by means of the apparatus. Furthermore, there is the wish to be able to generate the coffee extract with the fine-bubble froth layer in a manner in which the coffee extract jet may possibly have a smaller flow rate than the coffee extract jet in the known apparatus without adversely affecting the properties of the fine-bubble froth layer. This has the advantage that at the inlet a lower pressure is sufficient so that leakage less easily occurs.
The variation of the flow rate, more in particular the increase in flow rate, may be a result of, for instance, ageing of the apparatus. The apparatus is often provided with known per se means to supply coffee extract to the inlet under pressure. These known per se means, such as a Neapolitan apparatus or an apparatus comprising a pump for generating the pressure, have the property that the pressure of the coffee extract may vary. This variation may be connected with the age of the apparatus. This variation, however, is still much more connected with the thickness of a coffee bed through which hot water must be pressed to obtain the coffee extract supplied to the at least one inlet. When the thickness increases, the pressure drop over the coffee bed will increase, which has the result that the pressure of the coffee extract supplied to the inlet decreases. This means that the flow rate of the at least one coffee extract jet decreases. Also when the grain size of the ground coffee of the coffee bed decreases, the pressure drop over the coffee bed will increase, and the flow rate will thus decrease. It is therefore an object of the invention to make the characteristic properties of the formed fine-bubble froth layer less dependent on the flow rate of the coffee extract jet, and thus less dependent on the pressure of the coffee extract supplied to the inlet. It is thus ensured that the apparatus can properly function when using coffee beds having a varying thickness and grain size, and in apparatuses in which the pressure of the coffee extract supplied to the contents varies.
The apparatus according to the invention has for its object to provide a solution for the above wishes. Accordingly, the apparatus is characterized in that the impact surface, at least part of it, is provided with a roughened surface structure.
It appears that the impact surface having the roughened surface structure contributes to an increasing predictability of the fine-bubble froth layer, and that, moreover, the fine-bubble froth layer can be obtained at a smaller flow rate than that of the liquid jet in the known apparatus. This implies that the range of the flow rate of the liquid jet at which the fine-bubble froth layer can be obtained, increases with properties comparable to those of the fine-bubble froth layer obtained in the known apparatus. It even appears that the uniform character of the fine-bubble froth layer is improved. This has the result that the predictability of the fine-bubble froth layer increases because even at a varying flow rate, which flow rate, for whatever reason, decreases over time, the desired fine-bubble froth layer is obtained. It is not quite clear what processes take place on a microscale at the impact surface, which process contribute to obtaining a solution for the above wishes. The roughened surface structure will possibly cause very local turbulencenses in the coffee extract near the impact surface and/or limit liquid flows. Thee turbulences and/or limited liquid flows contribute to obtaining the desired predictable fine-bubble froth layer through, for instance, impingement of air.
Preferably, it holds that the surface structure has a surface roughness corresponding to the surface roughness of abrasive paper comprising particles having an average diameter of 50-2000 xcexcm. It appears that in this range of the surface roughness the desired effects are already well obtained.
In particular, it holds that the surface structure has a surface roughness corresponding to the surface roughness of abrasive paper in the range of P12 to P600. The P standard according to FEPA (Federation of European Producers of Abrasives) is used here. Preferably, it holds that the surface structure has a surface roughness corresponding to the surface roughness of abrasive paper in the range of P30 to P300. In this range of surface roughness, a fine-bubble froth layer is obtained with a desired optimum result. That is to say the fine-bubble froth layer is excellently predictable.
The roughened surface may be obtained in several ways. It is possible that the impact surface is subjected to a spark treatment. It is also possible, however, that the impact surface is sandblasted and/or chemically etched.
It also appears that it impossible that along the impact surface a gauze is provided to obtain the roughened surface structure. The gauze may have, for instance, the structure of the known per se aseptic gauze or sieve gauze and be made of metal. Preferably, it holds that in the at least one liquid flow path a receiving reservoir is included with an upright sidewall and a bottom, the bottom of the receiving reservoir forming the impact surface so that the at least one coffee extract jet, in use, squirts into the receiving reservoir. The size of the part of the surface provided with the roughened surface structure is, for instance, a circle having a diameter of about 2 cm.
The impact surface, that is to say the bottom of the receiving reservoir, may be directed such that a normal of the impact surface includes an angle A to the coffee extract jet which is less than 80xc2x0. In general, the coffee extract jet will be directed vertically; but this, too, is not necessary. The receiving reservoir may be of such design that it rapidly empties so that an, at least substantially, direct impingement of the at least one coffee extract jet on the part of the impact surface that comprises the roughened surface structure is continuously obtained. The buffer reservoir is at least substantially not filled. Due to this roughened surface, the fine-bubble froth layer is formed.
According to a special variant, after coffee extract has been supplied to the buffer reservoir for some time, in the receiving reservoir a liquid level will be formed at which the fine-bubble froth layer is then formed by impingement of the coffee extract jet on the liquid level. The roughened surface then has a liquid flow decelerating effect and thus enhances the formation of froth. It appears that in that case, also at a lower flow rate in the known apparatus, the desired fine-bubble froth layer is formed.
According to the invention, however, a receiving reservoir is not necessary. It is also possible that the impact surface only consists of a two-dimensional surface without upright side walls. The coffee extract can then, after an impingement of the coffee extract jet on the impact surface, flow away from the impact surface to the outlet. The fine-bubble froth layer is then formed again by local turbulences so that air is enclosed. A further advantage of this variant and the variant in which the receiving reservoir empties rapidly is that less afterflow results, the froth remains better intact, and a higher cup temperature can be achieved. To this end, a normal of the impact surface may include, for instance, an angle A to the coffee extract jet which is about equal to 45xc2x0.
According to a very advanced embodiment, it farther holds that in the variant provided with the receiving reservoir a liquid flow decelerating barrier located at a distance from the upright side walls is included in the receiving reservoir. Through the presence of the liquid flow decelerating barrier the liquid flow in the receiving reservoir is limited. The result is that the liquid level that may be formed in the receiving reservoir upon an impingement of the coffee extract jet on the layer of liquid in the receiving reservoir, has a calm less undulating ppearance than if the liquid flow decelerating barrier were not provided. The effect is therefore that liquid flows and turbulences on a macroscale in the receiving reservoir are reduced by the liquid flow decelerating barrier. It is shown by way of experiment that the range of the flow rate of the coffee extract jet in which the predictable uniform fine-bubble froth layer is formed is further increased. Also when the flow rate of the liquid extract jet increases relative to the flow rates providing the desired fine-bubble froth layer in the known apparatus, a very predictable fine-bubble froth layer is still obtained. Simultaneously, the roughened surface, on a microscale, provides small local turbulences, which also enhances the predictability and quality of the fine-bubble froth layer.
Preferably, it holds that the liquid flow decelerating barrier is included between a central part of the receiving reservoir and the upright side walls. Here, for instance, the coffee extract jet can impinge on the central part. To this end, the coffee extract jet is directed to the central part. It particulary holds that the receiving reservoir is provided with at least one liquid discharge path for discharging coffee extract from the receiving reservoir to the at least one outlet, while the at least one liquid discharge path originates outside, viewed from the central part, the liquid flow decelerating barrier. It appears that in this manner a, in use, very calm liquid discharge from the receiving reservoir to the at least one outlet is obtained, which has the result that an excellently predictable uniform fine-bubble froth layer is obtained which has a quality typified by connoisseurs as very good.
Preferably, it holds that the liquid flow decelerating barrier extends along a first closed curve extending around the central part.
In particular when it is desired to provide, for instance, two outlets with an equal amount of coffee extract, this embodiment is preferred because two liquid discharge paths can be symmetrically arranged in the apparatus which each originate outside, viewed from the central part, the liquid flow decelerating barrier, and which ach supply coffee extract with a fine-bubble froth layer to one of the two outlets, at an at least substantially equal flow rate.